This invention relates to hubs for securing and controlling rotors of a helicopter and more particularly to a hub including an elastomeric material which overcomes control problems.
Heretofore helicopter rotors have been secured to a rotatable shaft by various arrangements. Such arrangements use gimbals and other means which include bearings that make use of elastomeric material. It is well known in the prior art that operation of a helicopter creates conditions which exert G-forces on the fuselage, cause air and ground resonance, produce vibrations and many other problems.
Conventional articulated hubs require lag hinges to relieve coriolis and other lead-lag moments. Such hinges require lag dampers to prevent ground resonance. The coriolis forces also add together to cause in-plane hub loads. The low lag natural frequency causes the rotor blades to de-pattern in response to maneuvering acceleration transients, feeding forces back into the fuselage at right angles to the initial acceleration.
Soft in-plane hingeless rotors have no lag dampers but still have the same problems at set forth above. These problems also couple with in-flight rolling motion to produce a lightly damped or even unstable air resonance mode. Hingeless rotors also have strong gyroscopic coupling between pitch and roll control response and aircraft motions.